1. Technical Field
This disclosure relates to semiconductor chips and more particularly, to a method for creating silicided junctions and implanted junctions on the same semiconductor chip.
2. Description of the Related Art
Embedded memory chips have increasingly become more vital to high technology components. Embedded memory chips such as embedded dynamic random access memory (DRAM), refer to semiconductor chips that include logic circuits with memory arrays "embedded" therein. Embedded DRAM chips improve data transfer rates as well as increase bandwidth for the chip. Embedded DRAM chips have many applications in multimedia and communications.
Although embedded DRAM chips are desirable they are relatively more difficult to manufacture. Logic circuits generally require silicided junctions while memory arrays utilize implanted junctions. These two types of junctions are created using two different processes that are somewhat difficult to incorporate into a single process sequence. For example, the higher reaction temperatures needed to form the silicided junctions can present problems with respect to the integrity of the implanted junctions. Further, the silicide process and the implant process must be integrated without unduly complicating the process sequence or unduly increasing the number of thermal cycles required for the overall process. Ion implanted junctions are formed by bombarding the silicon surface with dopant ions. Ion implanted junctions do not have low sheet resistance as do silicided junctions. However, ion implanted junctions have controlled subsurface depth dopant concentrations.
Silicided junctions are formed in order to reduce sheet resistance over the semiconductor junction. A refractory metal is deposited on the surface of the semiconductor chip over a layer containing silicon. The refractory metal, for example, titanium or cobalt is reacted with the underlying layer containing silicon to form a silicide. The silicide formation at the silicon surface is determined by the metal silicon interface. The deposition of a highly pure metal and a clean surface are required for the silicide reaction. Any residues or contaminants lead to non-uniform silicide layers.
Therefore, a need exists for a semiconductor device in which silicided junctions and implanted junctions can be formed on the same semiconductor chip in a single process sequence.